diatoms are typical of newly setup tanks. I've had this in all of my S-T-S tanks. a quick remedy i've used is a powerhead with a filter attachment. Another more direct method was to use an aquarium vacuum attached to an airline running along the surface to siphon debris and diatoms. A third and last resort would be to do the one-two punch using hydrogen peroxide then excel...
"I am Groot", the faithful protector